Flat panel X-Ray detectors are in wide use in medicine. Most of these flat panel X-Ray detectors are based on a single light detector chip coupled with a scintillator. However, detectors of such a design are typically expensive. The single detector chip may be replaced by a plurality of less expensive optical sensors (e.g. CCD or CMOS) and lenses, which are arranged into a flat multi-camera array. X-Ray detectors including the multi-camera array may be less expensive in comparison with the single chip detectors since simpler sensors and lenses may be used. In multi-camera X-Ray detectors, each optical sensor acquires optical light irradiation from a segment of the scene as radiated from the scintillator. A complete image may be composed by stitching the plurality of partial images acquired by the plurality of single sensors.
The output image quality may be measured and assessed visually by visibility of the seam between the stitched partial images. Unfortunately, two neighbor images typically have intensity discrepancies in overlapping regions caused by differences in the relevant features of the sensors and their lenses, such as sensor's linearity of light-to-electrical transfer response, unity of optical performance of the lens, dark current, etc.
In addition, the acquired images may be distorted due to vignetting. A common effect of wide-angle and wide-aperture lenses is that the image tends to darken at the edges. This problem is generally referred as vignetting. Different variances of vignetting may include natural, optical, and mechanical vignetting. Vignetting is a result of undesired properties of the optical system due to light energy influx changes along the field of view (FOV) of the camera, caused by the optical system.
Stitching of images that were distorted by the vignetting effect may result in visible stitches in the complete image. Such an image may be visually unpleasant. Even worse, such a distorted image may make it difficult for a physician to visualize the true physiology of the patient and may lead to wrong diagnosis in some cases.
It would, therefore, be desirable to minimize and even completely eliminate the vignetting effect and produce a substantially seamless image.